A framing square is a long-armed tool having markings or indicia for measurement, which is suitable for marking and cutting lumber at specified angles, including right-angles and angles used for roof structures having various slopes. A framing square may also be referred to in the art as a steel square or carpenter's square. A framing square typically has two arms: a wider arm called a “blade” and a narrower arm called a “tongue,” which meet at a 90° angle. By aligning specific markings on the blade and the tongue with an edge of a piece of lumber, a builder can mark the lumber such that cutting along the mark forms a selected angle. Experienced builders can use a framing square to produce some roof structures without the need to calculate angles on paper.
Framing squares can be used to lay out common rafters, hip rafters, and stairs. Framing squares typically include standard roof framing tables of data to assist carpenters in determining how the framing square should be positioned to yield the selected angle for a particular application. For example, framing squares can include information on the length of a common rafter per foot of run, the length of a hip or valley rafter per foot of run, the difference in the length of jack rafters, side cut lengths, etc. Compound cuts can be made by setting a circular saw blade at a selected angle.
Property owners often request buildings having roofs with different shapes. The information on a conventional framing square does not enable even an experienced builder to cut lumber for all roof shapes without resorting to paper-based calculations, trial and error (i.e., make one cut, check to see if the lumber fits, and cut again as necessary), or cutting in place (e.g., high on a ladder or overhanging the edge of a roof structure).